AIDS is a worldwide health problem with 36 million people infected with HIV and estimated 5 million new infections occurring per year. These numbers indicate the need for a prophylactic vaccine to prevent the further spread of the disease. Despite tremendous efforts in AIDS vaccine research, traditional methods of vaccine development have failed to produce an effective vaccine for HIV infection. Recent vaccine efforts have focused on eliciting cellular immune responses directed against structural proteins of HIV instead/in addition to targeting humoral immune responses to the envelope. With that approach, adenoviral vector based vaccines have shown a great potential as vaccines for HIV in humans. Adenoviral vectors elicit strong innate immune responses, which greatly aid in inducing strong cellular immune responses. Moreover, adenoviruses are excellent as mucosal vaccines. However, one major drawback of adenoviral vaccines is prior immunity to adenoviruses in human, which could limit their efficacy. We propose to utilize a PEGylation technique to mask our Adeno-based AIDS vaccine vector, Ad/HIV, and test its efficacy in vivo. We propose to evaluate innate immune responses induced by the mucosal administration of PEGylated Ad/HIV (via intranasal route) and cellular immune responses (CTL and cytokine profiles) directed to HIV immunogen; gag encoded by the adenovector. In addition, we will determine both systemic and mucosal immune responses generated to PEGylated Ad/HIV. We will test the efficacy of PEGylated Ad/HIV both in naive mice and in mice with pre-existing immunity to adenoviruses. The results from this study will provide the groundwork for the development of a highly effective mucosal AIDS vaccine that can be repeatedly administered to patients with high efficacy.